Non-metallic conduit for electrical wiring is made with external ribs or rings and can be essentially rigid or somewhat flexible. As with metal flexible or solid conduit, one must be able to attach mechanically a length of the conduit to a connection box so that wires passing through the conduit can be connected to other wires or to an electrical device in the box. It is also desirable to be able to join mechanically lengths of conduit end-to-end.
The prior art devices for this purpose involve two or three pieces which go around the conduit and generally snap together. The conduit itself is made with annular protrusion and recesses on its exterior surface, the protrusions or rings being uniformly spaced along the conduit. Depending upon various factors, the conduit usually has about 84 to 92 rings per foot of conduit length. In the prior art connectors, one or more of the mating pieces contains a web which is designed to fit in a depression of the conduit between two adjacent rings. When the fitting parts are snapped together, the web in the depression holds the conduit in the fitting which can be either a connector which will connect the conduit to a box or a coupling which joins two pieces of conduit. Some of the connector type fittings do not require an additional piece to hold them together. The mating halves are brought together and inserted into a hole in the electrical box which holds them together. In other types, lock nuts are used to hold the mating components together.
These connectors have some disadvantages such as the difficulty of installation, particularly in cold weather. It is difficult to handle, manipulate and align the mating pieces when it is cold. It is also very easy to loose a mating piece.